Hard tissue formation in a porous HA/TCP ceramic scaffold loaded with stromal cells derived from dental pulp and bone marrow

\The aim of this study was to compare the ability of hard tissue regeneration of four types of stem cells or precursors under both in vitro and in vivo situations. Primary cultures of rat bone marrow, rat dental pulp, human bone marrow, and human dental pulp cells were seeded onto a porous ceramic scaffold material, and then either cultured in an osteogenic medium or subcutaneously implanted into nude mice. For cell culture, samples were collected at weeks 0, 1, 3, and 5. Results were analyzed by measuring cell proliferation rate and alkaline phosphatase activity, scanning electron microscopy, and real-time PCR. Samples from the implantation study were retrieved after 5 and 10 weeks and evaluated by histology and real-time PCR. The results indicated that in vitro abundant cell growth and mineralization of extracellular matrix was observed for all types of cells. However, in vivo matured bone formation was found only in the samples seeded with rat bone marrow stromal cells. Real-time PCR suggested that the expression of Runx2 and the expression osteocalcin were important for the differentiation of bone marrow stromal cells, while dentin sialophosphoprotein contributed to the odontogenic differentiation. In conclusion, the limited hard tissue regeneration ability of dental pulp stromal cells questions their practical application for complete tooth regeneration. Repeated cell passaging may explain the reduction of the osteogenic ability of both bone- and dentinal-derived stem cells. Therefore, it is essential to develop new cell culture methods to harvest the desired cell numbers while not obliterating the osteogenic potential.